3-D solid finite element for heterogeneous materials

The TFTR coils are composed of a bundle of copper windings which are bound together by insulation materials. A 3-D solid composite element is developed and implemented into the finite element code NASTRAN Level 16 for the stress analysis of the TFTR coils. One single element will be able to simulate the composite action of the copper/insulation bundle at stiffness generation and give detail stress distribution in both copper and insulation material at stress recovery. For heterogeneous material like the copper/insulation bundle, there are both strain and stress discontinuities across the interface of the two materials. In order to release the constraints at discontinuities, new shape functions are introduced. In this paper, the shortage of regular solid isoparametric elements in simulating composite action, the formulation of the composite element theory, the form of the new shape functions methods to introduce these shape functions into the element, and the method for stress recovery are discussed. In addition, example problems to validate the formulation and the implementation are presented